1. Field of the Invention
The present invention relates to a microphone apparatus built into an appliance which contains an acoustic noise or vibration source.
2. Description of the Prior Art
In collecting sound with a microphone, their resultant audio signals are frequently deteriorated in quality due to unwanted acoustic and vibration noises caused by the mechanical vibrations and wind noise. In particular, such an appliance as video camera produces a degree of unwanted noise and mechanical vibration depending on its moving mechanism contained in an enclosure. In common, when a noise source is located in a given direction for a microphone, a directional type microphone is employed and arranged to exhibit low sensitivity in the direction of the noise source and thus, permits its desired audio signal to be minimum affected by a noise from the noise source. For stereo sound recording, the use of directional microphones is essential. The disadvantage of such directional microphones mounted on the video camera is that the S/N ratio of a sound signal to be recorded is declined by the following facts.
The directional microphones are arranged adjacent to the noise source of the video camera and will be much affected by noise sounds from the noise source due to its proximity effect.
The directional microphones tend to be more affected by vibrations than non-directional microphones.
The directional microphones tend to be more affected by wind blow than non-directional microphones.
Some modified directional microphones capable of attenuating wind noises have been introduced. Such a microphone apparatus is disclosed in Japanese Patent Application Publication H01-39174 or 39195 (1989), which comprises a non-directional microphone, a unidirectional microphone, a lowpass filter for elimination of high frequency components of an output signal from the non-directional microphone, a lowpass filter for elimination of low frequency components of an output signal from the unidirectional microphone, an adder for summing two output signals of their respective filters, and a determining means for calculating the level of a wind noise.
In operation of the microphone apparatus, the output signal of the unidirectional microphone is selected for transmission if the wind noise level calculated by the determining means is low. If it is high, a sum signal of a high frequency component of the output signal of the unidirectional microphone and a low frequency component of the output signal of the non-directional microphone is selected for transmission. Accordingly, the microphone apparatus will be less affected by the wind noise than a traditional unidirectional microphone.
Although such a conventional microphone apparatus is capable of attenuating the level of an unwanted wind noise, when installed in a video camera, it is impossible to reduce the acoustic noise increasing due to the proximity effect and vibration noise when the level of wind noise is low.